Search

We report on the observation of a conspicuous loss in an ultracold mixture of $^{7}$Li and $^{88}$Sr atoms confined in a far-off-resonance optical dipole trap. We attribute the trap loss to the three-body inelastic Li-Sr-Sr collision and extract the corresponding three-body recombination coefficient $K_3$ at $T\sim 18.5,45,70,600$ $\mu K$. The measured three-body recombination coefficient is about two to three orders of magnitude larger than the typical values convenient for realizing quantum degenerate gases. It also indicates a potentially large $s$-wave scattering length between the bosonic $^{7}$Li and $^{88}$Sr atoms, and essentially rules out the prospect of realizing $^7$Li and $^{88}$Sr mixtures of high phase space density., Comment: 6 pages

Tests of the no-hair theorem using astrophysical black holes involve the detection of at least two quasi-normal modes (QNMs) in the gravitational wave emitted by a perturbed black hole. A detection of two modes -- the dominant, $(\ell, m, n) = (2,2,0)$, mode and its first overtone, the $(2,2,1)$ mode -- in the post-merger signal of the binary black hole merger GW150914 was claimed in Isi et al. [arXiv:1905.00869], with further evidence provided in Isi & Farr [arXiv:2202.02941]. However, Cotesta et al. [arXiv:2201.00822] disputed this claim, finding that evidence for the overtone only appeared if the signal was analyzed before merger, when a QNM description of the signal is not valid. Due to technical challenges, both of these analyses fixed the merger time and sky location of GW150914 when estimating the evidence for the overtone. At least some of the contention can be attributed to fixing these parameters. Here, we surmount this difficulty and fully marginalize over merger time and sky-location uncertainty while doing a post-merger QNM analysis of GW150914. We find that marginalizing over all parameters yields low evidence for the presence of the overtone, with a Bayes factor of $1.10\pm 0.03$ in favor of a QNM model with the overtone versus one without. The arrival time uncertainty of GW150914 is too large to definitively claim detection of the $(2,2,1)$ mode., Comment: 6 pages, 4 figures. Data available at https://zenodo.org/records/10493247

We revisit the recent debate on the evidence for an overtone in the black hole ringdown of GW150914. By gating and inpainting the data, we discard the contamination from earlier parts of the gravitational wave signal before ringdown. This enables the parameter estimation to be conducted in the frequency domain, which is mathematically equivalent to the time domain method. We keep the settings as similar as possible to the previous studies by \textcite{Cotesta:2022pci} and Isi \textit{et al.}\cite{Isi:2019aib,Isi:2022mhy} which yielded conflicting results on the Bayes factor of the overtone. We examine the spectral contents of the matched-filtering in the frequency domain, and propose a convergence test to assess the validity of an overtone model. Our results find the Bayes factors for the overtone fall within $10$ and $26$ around a range of times centered at the best-fit merger time of GW150914, which supports the existence of an overtone in agreement with the conclusions of Isi \textit{et al.}\cite{Isi:2019aib,Isi:2022mhy}. Our work contributes to the understanding of how various methods affect the statistical significance of overtones., Comment: 8 pages, 7 figures. Data release at https://github.com/gwastro/gw150914-overtone. Comments welcome!

We study Bayesian inference of black hole ringdown modes for simulated binary black hole signals. We consider to what extent different fundamental ringdown modes can be identified in the context of black hole spectroscopy. Our simulated signals are inspired by the high mass event GW190521. We find strong correlation between mass ratio and Bayes factors of the subdominant ringdown modes. The Bayes factor values and time dependency, and the peak time of the (3,3,0) mode align with those found analyzing the real event GW190521, particularly for high-mass ratio systems., Comment: 11 pages, 6 figures, 2 tables, accepted for publication in Phys. Rev. D

Searches for gravitational waves from compact-binary mergers, which to date have reported $\sim100$ observations, have previously ignored binaries whose components are both consistent with the mass of neutron stars $(1 M_\odot$ to $ 2 M_\odot)$ and have high dimensionless spin $>0.05$. While previous searches targeted sources that are representative of observed neutron star binaries in the galaxy, it is already known that neutron stars can regularly be spun up to a dimensionless spin of $\sim0.4$, and in principle reach up to $\sim0.7$ before breakup would occur. Furthermore, there may be primordial black hole binaries or exotic formation mechanisms to produce light black holes. In these cases, it is possible for the binary constituent to be spun up beyond that achievable by a neutron star. A single detection of this type of source would reveal a novel formation channel for compact-binaries. To determine if there is evidence for any such sources, we use PyCBC to conduct a targeted search of LIGO and Virgo data for light compact objects with high spin. Our analysis detects previously known observations GW170817 and GW200115; however, we report no additional mergers. The most significant candidate, not previously known, is consistent with the noise distribution, and so we constrain the merger rate of spinning light binaries., Comment: v3: add comparison with lvk subsolar search; accepted by MNRAS; 6 pages, 5 figures, 1 table; data release at https://github.com/gwastro/high-spin-light-binary

One of the major aims of gravitational wave astronomy is to observationally test the Kerr nature of black holes. The strongest such test, with minimal additional assumptions, is provided by observations of multiple ringdown modes, also known as black hole spectroscopy. For the gravitational wave merger event GW190521, we have previously claimed the detection of two ringdown modes emitted by the remnant black hole. In this paper we provide further evidence for the detection of multiple ringdown modes from this event. We analyse the recovery of simulated gravitational wave signals designed to replicate the ringdown properties of GW190521. We quantify how often our detection statistic reports strong evidence for a sub-dominant $(\ell,m,n)=(3,3,0)$ ringdown mode, even when no such mode is present in the simulated signal. We find this only occurs with a probability $\sim 0.02$, which is consistent with a Bayes factor of $56 \pm 1$ (1$\sigma$ uncertainty) found for GW190521. We also quantify our agnostic analysis of GW190521, in which no relationship is assumed between ringdown modes, and find that only 1 in 250 simulated signals without a $(3,3,0)$ mode yields a result as significant as GW190521. Conversely, we verify that when simulated signals do have an observable $(3,3,0)$ mode they consistently yield a strong evidence and significant agnostic results. We also find that constraints on deviations from the $(3,3,0)$ mode on GW190521-like signals with a $(3,3,0)$ mode are consistent with what was obtained from our previous analysis of GW190521. Our results strongly support our previous conclusion that the gravitational wave signal from GW190521 contains an observable sub-dominant $(\ell,m,n)=(3,3,0)$ mode., Comment: 16 pages, 10 figures

The recent discovery of a kilonova associated with an apparent long-duration gamma-ray burst has challenged the typical classification that long gamma-ray bursts originate from the core collapse of massive stars and short gamma-ray bursts are from compact binary coalescence. The kilonova indicates a neutron star merger origin and suggests the viability of gravitational-wave and long gamma-ray burst multimessenger astronomy. Gravitational waves play a crucial role by providing independent information for the source properties. This work revisits the archival 2015-2020 LIGO/Virgo gravitational-wave candidates from the 4-OGC catalog which are consistent with a binary neutron star or neutron star-black hole merger and the long-duration gamma-ray bursts from the Fermi-GBM and Swift-BAT catalogs. We search for spatial and temporal coincidence with up to 10 s time lag between gravitational-wave candidates and the onset of long-duration gamma-ray bursts. The most significant candidate association has only a false alarm rate of once every two years; given the LIGO/Virgo observational period, this is consistent with a null result. We report an exclusion distance for each search candidate for a fiducial gravitational-wave signal and conservative viewing angle assumptions., Comment: v2: 8 pages, 2 figures, 1 table. Referee comments addressed. ApjL in press. Data released in https://github.com/gwastro/gw-longgrb

We use the monodromy method to investigate the asymptotic quasinormal modes of regular black holes based on the explicit Stokes portraits. We find that, for regular black holes with spherical symmetry and a single shape function, the analytical forms of the asymptotic frequency spectrum are not universal and do not depend on the multipole number but on the presence of complex singularities and the trajectory of asymptotic solutions along the Stokes lines., Comment: 35 pages, 31 figures, add some references, accepted by Chinese Physics C

Advanced LIGO and Virgo have reported 90 confident gravitational-wave (GW) observations from compact-binary coalescences from their three observation runs. In addition, numerous subthreshold gravitational-wave candidates have been identified. Binary neutron star (BNS) mergers can produce gravitational waves and short-gamma ray bursts, as confirmed by GW170817/GRB 170817A. There may be electromagnetic counterparts recorded in archival observations associated with subthreshold gravitational-wave candidates. The CHIME/FRB Collaboration has reported the first large sample of fast radio bursts (FRBs), millisecond radio transients detected up to cosmological distances; a fraction of these may be associated with BNS mergers. This work searches for coincident gravitational waves and FRBs from BNS mergers using candidates from the fourth-Open Gravitational-wave Catalog (4-OGC) and the first CHIME/FRB catalog. We use a ranking statistic for GW/FRB association which combines the gravitational-wave detection statistic with the odds of temporal and spatial association. We analyze gravitational-wave candidates and non-repeating FRBs from 2019 April 1 to 2019 July 1, when both the Advanced LIGO/Virgo gravitational-wave detectors and the CHIME radio telescope were observing. The most significant coincident candidate has a false alarm rate of 0.29 per observation time, which is consistent with a null observation. The null results imply, at most, $\mathcal{O}(0.01)\%$ - $\mathcal{O}(1)\%$ of FRBs are produced from the BNS mergers., Comment: v2: 8 pages, 2 figures, 1 table; add explicit computation for event rate estimate; update to match the published version of ApJ. Data and scripts released in https://github.com/gwastro/gwfrb-4ogc-chime

We present a search for gravitational waves from the coalescence of binaries which contain at least one subsolar mass component using data from the LIGO and Virgo observatories through the completion of their third observing run. The observation of a merger with a component below $1\,M_{\odot}$ would be a clear sign of either new physics or the existence of a primordial black hole population; these black holes could also contribute to the dark matter distribution. Our search targets binaries where the primary has mass $M_1$ between 0.1-100$\,M_{\odot}$ and the secondary has mass $M_2$ from 0.1-1$\,M_{\odot}$ for $M_1 < 20\,M_\odot$ and 0.01-1$\,M_{\odot}$ for $M_1 \ge 20\,M_\odot$. Sources with $M_1 < 7\,M_\odot, M_2 > 0.5\,M_\odot$ are also allowed to have orbital eccentricity up to $e_{10} \sim 0.3$. This search region covers from comparable to extreme mass ratio sources up to $10^4:1$. We find no statistically convincing candidates and so place new upper limits on the rate of mergers; our analysis sets the first limits for most subsolar sources with $7\,M_{\odot}< M_1 < 20\,M_{\odot}$ and tightens limits by $\sim 8\times$ $(1.6\times)$ where $M_1 > 20\,M_{\odot}$ ($M_1 < 7\,M_{\odot}$). Using these limits, we constrain the dark matter fraction to below 0.3 (0.7)$\%$ for 1 (0.5)$\,M_{\odot}$ black holes assuming a monochromatic mass function. Due to the high merger rate of primordial black holes beyond the individual source horizon distance, we also use the lack of an observed stochastic background as a complementary probe to limit the dark matter fraction. We find that although the limits are in general weaker than those from the direct search they become comparable at $0.1 \,M_{\odot}$., Comment: 5 pages excluding references, 3 figures, comments welcome. Supplementary material at https://github.com/gwastro/subsolar-O3-search

We present the fourth Open Gravitational-wave Catalog (4-OGC) of binary neutron star (BNS), binary black hole (BBH) and neutron star-black hole (NSBH) mergers. The catalog includes observations from 2015-2020 covering the first through third observing runs (O1, O2, O3a, O3b) of Advanced LIGO and Advanced Virgo. The updated catalog includes 7 BBH mergers which were not previously reported with high significance during O3b for a total of 94 observations: 90 BBHs, 2 NSBHs, and 2 BNSs. The most confident new detection, GW200318_191337, has component masses $49.1^{+16.4}_{-12.0}\textrm{M}_\odot$ and $31.6^{+12.0}_{-11.6}\textrm{M}_\odot$; its redshift of $0.84^{+0.4}_{-0.35}$ ($90\%$ credible interval) may make it the most distant merger so far. We estimate the merger rate of BBH sources, assuming a powerlaw mass distribution containing an additive Gaussian peak, to be $16.5_{-6.2}^{+10.4} (25.0_{-8.0}^{+12.6})$ Gpc$^{-3}$ yr$^{-1}$ at a redshift of $z=0$ ($0.2$). For BNS and NSBH sources, we estimate a merger rate of $200^{+309}_{-148}$ Gpc$^{-3}$ yr$^{-1}$ and $19^{+30}_{-14}$ Gpc$^{-3}$ yr$^{-1}$, respectively, assuming the known sources are representative of the total population. We provide reference parameter estimates for each of these sources using an up-to-date model accounting for instrumental calibration uncertainty. The corresponding data release also includes our full set of sub-threshold candidates., Comment: v2, 22 pages, 7 figures, 5 tables, data release at https://github.com/gwastro/4-ogc, submitted to ApJ, comments welcome

We report the results of testing gravitational-wave birefringence using the largest population of gravitational-wave events currently available. Gravitational-wave birefringence, which can arise from the effective field theory extension of general relativity, occurs when the parity symmetry is broken, causing the left- and right-handed polarizations to propagate following different equations of motion. We perform Bayesian inference on the 94 events reported by the 4th-Open Gravitational-wave Catalog (4-OGC) using a parity-violating waveform. We find no evidence for a violation of general relativity in the vast majority of events. However, the most massive event, GW190521, and the second most massive event, GW191109, show intriguing non-zero results for gravitational-wave birefringence. We find that the probability of association between GW190521 and the possible electromagnetic (EM) counterpart reported by Zwicky Transient Facility (ZTF) is increased when assuming birefringence. Excluding GW190521 and GW191109, the parity-violating energy scale is constrained to $M_\mathrm{PV} > 0.05$ GeV at $90\%$ credible interval, which is an improvement over previous results from twelve events by a factor of five. We discuss the implications of our results on modified gravity and possible alternative explanations such as waveform systematics. More detections of massive binary black hole mergers from the upcoming LIGO/Virgo/KAGRA run will shed light on the true origin of the apparent birefringence., Comment: v4: 9 pages, 4 figures; Testing GR with 94 GW events, 2 outliers. Update to match the published version in PRD. Code & data release in https://github.com/gwastro/4ogc-birefringence

We introduce a concept of ridge-lines to investigate the semi-classical prediction from wave-packets with arbitrary width in conventional quantum mechanics and the Wheeler--DeWitt quantum cosmology. Two primary approaches are applied to the exact calculation of the ridge-lines, namely the contour and the stream approach. Moreover, aspects of these are discussed and compared to other scenarios and approaches, i.e. the narrow WKB wave-packets and the first-derivative test. As the main result, we show that the semi-classical predictions in toy models have more abundant solutions than in the classical theory, and most interestingly they may deviate from classical solutions due to the quantum corrections., Comment: 44 pages, 14 figures, 3 tables

We present a search for gravitational waves from the coalescence of sub-solar mass black hole binaries using data from the first half of Advanced LIGO and Virgo's third observing run. The observation of a sub-solar mass black hole merger may be an indication of primordial origin; primordial black holes may contribute to the dark matter distribution. We search for black hole mergers where the primary mass is $0.1-7 M_{\odot}$ and the secondary mass is $0.1-1 M_{\odot}$. A variety of models predict the production and coalescence of binaries containing primordial black holes; some involve dynamical assembly which may allow for residual eccentricity to be observed. For component masses $>0.5 M_{\odot}$, we also search for sources in eccentric orbits, measured at a reference gravitational-wave frequency of 10 Hz, up to $e_{10}\sim 0.3$. We find no convincing candidates and place new upper limits on the rate of primordial black hole mergers. The merger rate of 0.5-0.5 (1.0-1.0)~$M_{\odot}$ sources is $<7100~(1200)$ Gpc$^{-3}$yr$^{-1}$. Our limits are $\sim3-4$ times more constraining than prior analyses. Finally, we demonstrate how our limits can be used to constrain arbitrary models of the primordial black hole mass distribution and merger rate., Comment: 7 pages, 3 figures, 1 table, v3 updated to match PRL, supplementary materials at https://github.com/gwastro/subsolar-o3a-search

We present the third Open Gravitational-wave Catalog (3-OGC) of compact-binary coalescences, based on the analysis of the public LIGO and Virgo data from 2015 through 2019 (O1, O2, O3a). Our updated catalog includes a population of 57 observations, including four binary black hole mergers that had not previously been reported. This consists of 55 binary black hole mergers and the two binary neutron star mergers GW170817 and GW190425. We find no additional significant binary neutron star or neutron star--black hole merger events. The most confident new detection is the binary black hole merger GW190925\_232845 which was observed by the LIGO Hanford and Virgo observatories with $\mathcal{P}_{\textrm{astro}} > 0.99$; its primary and secondary component masses are $20.2^{+3.9}_{-2.5} M_{\odot}$ and $15.6^{+2.1}_{-2.6} M_{\odot}$, respectively. We estimate the parameters of all binary black hole events using an up-to-date waveform model that includes both sub-dominant harmonics and precession effects. To enable deep follow-up as our understanding of the underlying populations evolves, we make available our comprehensive catalog of events, including the sub-threshold population of candidates, and the posterior samples of our source parameter estimates., Comment: 17 pages, 5 figures, 4 tables, v3 updated to match ApJ accepted version. Supplementary material at https://github.com/gwastro/3-ogc

When two black holes merge, the late stage of gravitational wave emission is a superposition of exponentially damped sinusoids. According to the black hole no-hair theorem, this ringdown spectrum depends only on the mass and angular momentum of the final black hole. An observation of more than one ringdown mode can test this fundamental prediction of general relativity. Here we provide strong observational evidence for a multimode black hole ringdown spectrum using the gravitational wave event GW190521, with a maximum Bayes factor of $56\pm1$ ($1\sigma$ uncertainty) preferring two fundamental modes over one. The dominant mode is the $\ell=m=2$ harmonic, and the sub-dominant mode corresponds to the $\ell=m=3$ harmonic. The amplitude of this mode relative to the dominant harmonic is estimated to be $A_{330}/A_{220} = 0.2^{+0.2}_{-0.1}$. We estimate the redshifted mass and dimensionless spin of the final black hole as $330_{-40}^{+30}~\mathrm{M}_{\odot}$ and $0.86_{-0.11}^{+0.06}$, respectively. We find that the final black hole is consistent with the no hair theorem and constrain the fractional deviation from general relativity of the sub-dominant mode's frequency to be $-0.01^{+0.08}_{-0.09}$., Comment: Accepted for publication in PRL. 7 pages, 4 figures, plus supplemental. Data available at https://github.com/gwastro/BH-Spectroscopy-GW190521

We present the first search for gravitational waves from sub-solar mass compact-binary mergers which allows for non-negligible orbital eccentricity. Sub-solar mass black holes are a signature of primordial origin black holes, which may be a component of dark matter. To produce binary coalescences, primordial black holes may form close binaries either in the early universe or more recently through dynamical interactions. A signature of dynamical formation would be the observation of non-circularized orbits. We search for black hole mergers where the primary mass is $0.1-7 M_{\odot}$ and the secondary mass is $0.1-1 M_{\odot}$. We allow for eccentricity up to $\sim0.3$ at a dominant-mode gravitational-wave frequency of 10 Hz for binaries with at least one component with mass $>0.5 M_{\odot}$. We find no convincing candidates in the public LIGO data. The two most promising candidates have a false alarm rate of 1 per 3 and 4 years, respectively, which combined is only a $\sim 2.4\sigma$ deviation from the expected Poisson rate. Given the marginal statistical significance, we place upper limits on the rate of sub-solar mass mergers under the assumption of a null observation and compare how these limits may inform the possible dark matter contribution., Comment: 7 pages, 4 figures, 1 table. Supplementary material at https://github.com/gwastro/subsolar-ecc-primordial-search, v2 fixes minor typos